1. Technical Field
The invention is directed to a flexible joining device for use with conveyor belts.
2. Prior Art
Conveyor belts are used in various industries for carrying materials and matters, generally, but not necessarily, in bulk form. Most often these conveyor belts are made up of a flexible material, having a certain elasticity, at least in the longitudinal direction, and they require the junction of the two ends, to constitute an endless conveyor belt, which passes around rollers, at least one of them being a driving roller the other one being generally a free roller known as idle roller.
In what concerns the methods of joining these conveyor belts, two main families are known hitherto.
A first family consists in sticking or vulcanizing the conveyor belt ends, when the band or the belt contains a large proportion of rubber. The operating conditions for presenting these ends and the operating conditions for carrying out the sticking or the vulcanization of these ends, one to the other, are well known by the men of the art.
The other family of joining methods makes use of joining devices consisting in a series of rigid metallic staples, usually U-shaped, each comprising two fixing lugs and an eyelet at their internal concave part, thus forming a so-called knuckle, similar to hinges. The fixing lugs of these rigid staples are attached to one end of the conveyor belt, one of them being fixed on one of the end faces of the conveyor belt, the other one on the other end face of the conveyor, by means of rivets or by means of spikes, often dual type spikes the sharp-pointed free ends of which are turned down after crossing matching holes, one of the lugs, the band and the other lug, then projecting from this latter.
The first family of joining methods, suffers of the major inconvenience resulting from the length of the operations, requiring a rather long shut-down, which may last up to 24 hours, and on the other hand from the difficulty often encountered in the hard running conditions (prevailing in transport of materials, and certain production industries) detrimental to a proper performance of the preparation of the ends. Furthermore, these junctions are not detachable. The possibility of carrying out a disconnection is useful, if a conveyor belt device has to be lengthened, which is often the case in mines, in quarries and in public works, along with the advance of the mine working face, the quarries works of the public works. Also, an easy disconnection enables an easy replacement of a piece of worn or damaged belt, the remaining pieces being usable.
In the case of the second family of joining methods, the operation can be faster and require a less careful preparation of the conveyor belt ends. However these junctions present major drawbacks which consist essentially in two problems. The first one lies in the fact that the linking and hinging axis is worn by the staples which are hinged upon it, and rotate with respect to it, during the running of the conveyor belt. This is unavoidable owing to the inherent design of the joining devices. Some corrective measures have been envisaged in order to obviate such wear, but these measures are either inefficient, or they increase considerably the cost, while they are far from totally effective.
The second problem encountered with the method of joining according to the second family, results from tears in the belt ends caused by the nails or points positioned rather close to the extremity of the belt ends. Due to their stiffness, the fixing lugs of the staples must be short in order to match more or less with the curve of the belt when the latter moves over a roller (either driving or idle), thus requiring as mentioned hereabove the location of the points or the rivets, rather close to the ends of the belt. Moreover, owing to this stiffness, the points are submitted to hard tensions, the path of the lug located on the roller side being shorter than the path of the lug located on the external side. The hard tensions which are supported by the points owing to the stiffness of the fixing lugs, cause the slow tear of the conveyor belt by the rivet or spike stem which crosses through the belt, and the failure of the junction.